(1) Field of the Invention
The present invention relates to a liquid crystal display device and to a technology for adjusting the distance between a TFT substrate and a facing substrate using a spacer in a configuration where the space between the TFT substrate and the facing substrate is filled in with liquid crystal in accordance with a liquid crystal dropping and sealing method.
(2) Related Art Statement
In liquid crystal display devices, the space between the TFT substrate on which pixel electrodes and thin film transistors (TFT's) are formed and the facing substrate where color filters and the like are formed is filled in with liquid crystal, and an image is formed by controlling the molecules in this liquid crystal using an electrical field. The distance between the TFT substrate and the facing substrate is as small as several microns. In accordance with conventional methods for filling in the space between the substrates with liquid crystal, the space between the TFT substrate and the facing substrate is sealed with a sealing material and the inside made a vacuum, and liquid crystal is injected through an inlet for liquid crystal provided in a portion of the sealing material using the ambient pressure.
When the distance between the TFT substrate and the facing substrate is small and the display area of the liquid crystal display device is large, however, it takes a long time to inject liquid crystal, making the throughput in the manufacture longer, and thus increasing the cost of manufacture. As a measure against this, a technology where a necessary amount of liquid crystal is dropped on a facing substrate (or TFT substrate) where a sealing material is formed in closed annular form in the periphery portion, and after that the TFT substrate (or facing substrate) is pasted to the other substrate so that the liquid crystal is sealed in (liquid crystal dropping and sealing method) has been developed.
The distance between the TFT substrate and the facing substrate is kept constant by dispersing small beads according to the prior art. In the case where beads are dispersed in accordance with a liquid crystal dropping and sealing method, however, beads move when liquid crystal is dropped, causing there to be places with many beads and places with few beads. Thus, the distance between the TFT substrate and the facing substrate becomes inconsistent. When the distance between the TFT substrate and the facing substrate becomes inconsistent, such a problem arises that the contrast of images in the liquid crystal display device lowers and the pixels become inconsistent.
Meanwhile, a method for forming support columns of an organic film on the facing substrate (support column method) has been developed as a method for controlling the distance between the TFT substrate and the facing substrate. The support columns are secured to the facing substrate, and therefore, do not move when liquid crystal is dropped onto the substrate. Accordingly, the method for controlling the distance using support columns is appropriate in the method for dropping liquid crystal (liquid crystal dropping and sealing method).
A number of conductive layers for forming TFT's, video signal lines, scanning lines, electrodes and the like are formed on the TFT substrate, and contact holes for connecting conductive layers are created. The portions where the contact holes are created are recesses. Meanwhile, the support columns are formed on the facing substrate. When the support columns enter the contact hole portions, the distance between the TFT substrate and the facing substrate cannot be kept constant. “Patent Document 1” describes a configuration where there are support columns which engage or do not engage with contact holes. “Patent Document 1” describes that it is better for the support columns not to enter into contact holes, but even in the case where some support columns do enter into contact holes, due to the TFT substrate and the facing substrate shifting in position, the remaining support columns, which do not enter into contact holes, keep the distance between the TFT substrate and the facing substrate constant. In “Patent Document 1,” the contact hole portions ideally do not to have a support column, and therefore, support columns are located in the peripheral portion of the contact holes, even in the case where there are some support columns in contact portions.
In addition to contact holes portions on the TFT substrate, protrusions are formed in portions where wires cross, and thus, the surface is not flat. “Patent Document 2” describes a configuration where support columns of a constant height are formed on the facing substrate so that some support columns make contact with flat portions on the TFT substrate and other support columns make contact with protrusions. That is to say, some support columns are compressed by the height of protruding wires and the like, so that the degree of compression functions as a so-called gravity margin. In this case, the amount by which the support columns are compressed is approximately 200 nm to 600 nm.
(Patent Document 1) Japanese Unexamined Patent Publication 2005-345819 (Corresponding U.S. Application US2005/0270471 A1)
(Patent Document 2) Japanese Unexamined Patent Publication 2005-242310 (Corresponding U.S. Application US2005/0190338 A1)